1. Field of the Invention
This invention relates to an improvement of a structure of fixing a back core, forming a closed magnetic circuit by being positioned at an open end of a pair of magnetic cores defining a magnetic gap, to the magnetic cores.
2. Description of the Prior Art
A conventional back core fixing structure of magnetic head is shown in FIG. 5. This fixing structure is of the type applied to a combined type magnetic head. The combined type magnetic head is composed of a recording/reproducing magnetic head core assembly 11 and an erase magnetic head core assembly 21 coupled together via a non-magnetic substance 31, such as ceramics or glass. The recording/reproducing magnetic head core assembly 11 or the erase magnetic head core assembly 21 is composed of a pair of magnetic cores 12 and 13 or of a pair of magnetic cores 22 and 23 joined together, and a space between the magnetic cores of either pair defines a recording/reproducing gap 10 or an erase gap 20. Within the space of either the recording/reproducing gap 10 or the erase gap 20 is interposed a non-magnetic material such as glass of high melting point. The erase gap 20 is for creating no-record bands on either side of a recording track recorded by the recording/reproducing gap 10.
The core 13 of the recording/reproducing magnetic head core assembly or the core 23 of the erase magnetic head core assembly has a coil bobbin 15 or 25 fitted thereon, and the coil bobbin 15 or 25 has a coil 16 or 26 wound therearound. FIG. 5 shows only one set of bobbin and coil. Sliders 35 and 35 are joined to either side of the recording/reproducing magnetic core assembly 11 and erase magnetic core assembly 21.
A back core 41 is joined to both the magnetic cores 12 and 13 and to both the magnetic cores 22 and 23. This back core 41 is formed into the shape of a single body by magnetic materials 43 and 44 joined together with interposition of non-magnetic material 42 therebetween, and the non-magnetic material 42 corresponds to the non-magnetic substance 31 interposed between the joined portions of the magnetic core 12 and the magnetic core 22. The back core 41 is joined to one side surface of the open end, i.e. of the opposite side of the recording/reproducing magnetic head core assembly 11 and erase magnetic head core assembly 21 to the confronting side facing opposite a magnetic medium, and to achieve such joining, a holding member 51 is used. This holding member 51 has an L-shaped face section 52 held in contact with the open end surface and one side surface of the recording/reproducing magnetic head core assembly 11 and erase magnetic head core assembly 21, and a pair of resilient tongue segments 53 having pinching power which extend downward in the drawing from edge portions of the face section 52. After the back core 41 is disposed at a predetermined position, i.e. on one side surface of the open end of the recording/reproducing magnetic head core assembly 11 and erase magnetic head core assembly 21 and the non-magnetic material 42 is aligned in position with the non-magnetic substance 31, the back core 41 is attached so as to cover the back core 41 from the open end of the recording/reproducing magnetic head core assembly 11 and erase magnetic head core assembly 21, and is fixed to the recording/reproducing magnetic head core assembly 11 and the erase magnetic head core assembly 21 by means of the pinching power of the resilient tongue segments 53. The fixing of the back core 41 to the recording/reproducing magnetic head core assembly 11 and the erase magnetic head core assembly 21 may be achieved by the use of bond, such as adhesive or synthetic resin. As the back core 41 is fixed to the recording/reproducing magnetic head core assembly 11 and the erase magnetic head core assembly 21, a closed recording/reproducing magnetic circuit is formed by the magnetic cores 12 and 13 and the magnetic material 44, whereas a closed erase magnetic circuit is formed by the magnetic cores 22 and 23 and the magnetic material 43.
According to the conventional back core fixing structure described above, the back core 41 is disposed on the recording/reproducing magnetic head core assembly 11 and the erase magnetic head core assembly 21, and the holding member 51 is attached from above both the core assemblies in the drawing (from the side of the open end) with the point of each resilient tongue segment 53 being oriented toward the confronting surface side of the recording/reproducing magnetic head core assembly 11 and erase magnetic head core assembly 21 so as to pinch and fix the back core 41 to both the core assemblies. Thus, the holding member 51 covers the position setting portions of the non-magnetic material 42 and the non-magnetic substance 31, thereby making difficult fixing work. Further, if the pinching power of the resilient tongue segments 53 is weak, the joined state of the back core 41 is loose to influence the closed magnetic circuits. Furthermore, since the resilient tongue segments 53 extend from end portions of the face section 52, the pinching power of the resilient tongue segments 53 acts strongly on the magnetic cores 13 and 23, but weakly on the magnetic cores 12 and 22 to thereby weaken the joined state. Still more, in case the back core 41 is fixed by the use of bond, a long time is necessary for the bond to solidify, thus, a different holding jig must be used to keep the joined state until the bond solidifies. In addition, since the bond is interposed between the back core 41 and the recording/reproducing magnetic head core assembly 11 and erase magnetic head core assembly 21, there is involved the problem that some loss is created in each magnetic circuit and the like.